Conventionally, when a wellbore is created, a number of casings are installed in the borehole to prevent collapse of the borehole wall and to prevent undesired outflow of drilling fluid into the formation or inflow of fluid from the formation into the borehole. The borehole is drilled in intervals whereby a casing which is to be installed in a lower borehole interval is lowered through a previously installed casing of an upper borehole interval. As a consequence of this procedure the casing of the lower interval is of smaller diameter than the casing of the upper interval. Thus, the casings are in a nested arrangement with casing diameters decreasing in downward direction. Cement annuli are provided between the outer surfaces of the casings and the borehole wall to seal the casings from the borehole wall. As a consequence of this nested arrangement a relatively large borehole diameter is required at the upper part of the wellbore. Such a large borehole diameter involves increased costs due to heavy casing handling equipment, large drill bits and increased volumes of drilling fluid and drill cuttings. Moreover, increased drilling rig time is involved due to required cement pumping and cement hardening.
International patent application WO 93/25799 discloses a method of creating a casing in a section of a borehole formed in an underground formation, wherein a tubular element in the form of a casing is installed within the section of the borehole, and radially expanded using an expansion mandrel. Expansion of the casing continues until the casing contacts the borehole wall and elastically deforms the surrounding rock formation. Optionally, when washouts occur in the borehole wall during drilling, or when brittle formations are encountered during drilling, cement is pumped in an annular space around the casing at the location of such washout or brittle formation.
Although the known method overcomes the problem of conventional casings whereby the diameter of subsequent casing sections decreases in downward direction, there remains a need for a method of creating a casing in a borehole, whereby a lower load is required to expand the tubular element, and whereby an improved sealing between the casing and the surrounding earth formation is achieved.
In WO 93/25800 an application of a production liner in a borehole is disclosed, the production liner provided with longitudinally overlapping openings and is radially expanded in the borehole. The production liner serves as a strainer during production of hydrocarbon fluid flowing from the surrounding earth formation through the openings, into the liner. It is essential for this production liner that fluid communication is maintained between the interior of the liner and the surrounding earth formation, i.e. it is essential that the occurrence of a sealing between the production liner and the surrounding formation is avoided. This is contrary to the object of the present invention which is aimed at providing an improved sealing between the casing and the surrounding earth formation. It is another object of the invention to provide a method of creating a casing having an improved collapse resistance. A further object of the invention is to provide a method of creating a casing which allows a smaller difference in borehole diameter between an upper interval and a lower interval of the borehole.